Development of a HIV-1 vaccine to prevent, or reduce, the rate of infection remains a high priority. The lessons from numerous failed and the recent modestly successful RV144 Thai trial indicate the need to advance new approaches to HIV-1 vaccine design with the goal of inducing immune responses that are the appropriate type, quality, magnitude and active in the appropriate sites in the body. Our strategy is to build upon the RV144 study which implemented a canarypox vector prime (T and B cell immunogens) followed by a recombinant envelope (Env) protein boost immunization. The primary objective of this project is to assess an immunization strategy to induce broadly neutralizing antibodies (BnAbs) in nonhuman primates based on vaccines containing recombinant simian adenovirus (SAd) viral vectors and HIV-1 Env glycoproteins selected from sequential isolates of an HIV-1-infected individual that ultimately developed CD4-binding site BnAbs. The premise of this approach is to engage naive B-cell receptors of BnAbs, and continue to immunize with select immunogens to stimulate somatic mutation that leads to induction of BnAbs. Our central hypothesis is that the combination of replicating adenovirus persistently expressing Envs selected at critical junctions during development of BnAbs will be efficient vaccine immunogens for inducing protective antibodies against HIV-1 infection. It will be evaluated whether serial or swarm immunization with SAds expressing Envs delivered with matching Env glycoprotein immunogens can induce BnAbs. The recombinant SAdEnv vectors will be assessed for immunogenicity in rabbits before proceeding to NHP studies in Year 2. Both antibody (binding, neutralizing, and ADCVI) and Env-specific T cell immune responses will be evaluated. Completion of this SBIR II program may provide sufficient data to determine the utility of the replicating adenovirus vector system for expressing B cell lineage Envs and potentially could yield an experimental vaccine suitable for clinical development.